Aspects of point sources and line sources in the artificial initiation of vibration by vibration generators

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16th D-A-CH Conference on Earthquake Engineering and Structural Dynamics

For the meeting in September 2019 our experts Michael Österreicher and Wolfgang Unterberger prepared a contribution on the subject of “Earthquake Engineering and Structural Dynamics”.

In the course of constructing a new railway line, vibration and structure-borne sound play an integral part in the planning process. Appropriate counter-measures (such as mass-spring systems) must be considered as early as the design phase because these can have a significant influence on such decisions as the cross-sectional dimension of the excavation. This initial dimensioning is mostly carried out via geodynamic testing and modelling. However, any tests that take place before the start of construction work are plagued by a range of uncertainties as a result of which verification measurements are required after the completion of tunnels and substructures and before any traffic can pass through it in order to recheck the planned measures. One method of doing this is to trigger artificial vibrations in tunnel shells and substructures with the help of vibration generators while, simultaneously, taking vibration measurements at the source and in neighbouring objects. These vibrations are generally initiated by vibration generators from the field of seismic exploration. However, in carrying out this work it has to be taken into consideration that, as vibration generators are point sources, the vibrations that they initiate are different from those produced by moving trains.

This (german) study involves a detailed investigation of the different vibrations triggered by point sources and line sources. It then presents a methodology, which makes it possible to convert the immissions provided by a vibration generator into the real vibrations caused by a train. By taking into account the transmission function and local admittances the method uses superposition to recalculate the vibrations measured from the point source into the vibrations created by a line source that is comparable with a train.